This invention relates to a method for removing deposits from contact lenses of a polymeric material, particularly deposits of lipids from contact lenses wherein at least a portion of the polymeric material is an organosilicon compound, by contacting the contact lens surfaces with certain volatile methylsiloxane fluids such as octamethylcyclotetrasiloxane and thereafter removing the fluid and the lipids from the contact lens.
During use, contact lenses are known to acquire deposits of proteins, lipids and inorganic salts from the tear fluid and secretions of the eye. A number of commercially available contact lens cleaning solutions and cleaning regimens are available to remove such deposits with varying degrees of success. To be useful, the polymeric material from which the contact lens is made must be sufficiently wettable by human tears to be worn on the eye. If these deposits are allowed to build up, the contact lens eventually loses its wettability, optical clarity, or physiological compatibility, thereby becoming a non-functional contact lens.
The formation of deposits on the exposed surfaces of polymeric contact lenses involves a complex interaction between polymeric contact lens material (having a particular surface energy), the wearer's tear liquid composition (unique to each person), the tear liquid surface tension, and the polymeric lens material/tear liquid interfacial forces. These variables interact to determine the nature of the tear liquid components which predominate as accumulated deposits on the lens surfaces. It can be generalized that "like materials have an affinity to be preferentially attracted to one another".
Organic polar polymeric materials tend to attract proteins and salts which can be removed by aqueous contact lens cleaners containing nonionic surfactants and in the case of protein deposits, protein-digesting enzymatic cleaners are available. Water absorbing, soft contact lenses which are generally copolymers of hydrophilic, aliphatically unsaturated, organic compounds such as 2-hydroxyethyl methacrylate or N-vinyl pyrrolidone with difunctional cross-linking compounds such as triethylene glycol diacrylate (e.g., see U.S. Pat. No. Re. 27,401 to Wichterle, et al., issued June 20, 1972) are more prone to attracting deposits of proteins and salts which are at least somewhat polar in nature and therefore associate with the polar radicals present in the polymeric contact lens material.
A problem occurs when lipid deposits are present on the contact lens surface because lipid deposits tend to be nonpolar and hydrophobic in nature. Nonionic surfactant type contact lens cleaners do not remove lipids as well as proteins and salts. Enzymatic cleaners do not, to any great extent, remove lipid deposits such as cholesterol esters and the various other sterol esters, wax esters, free acids and triglycerides known to be deposited on contact lenses. Peroxides and bleaches are not very effective and abrasive cleaners can alter the optical surface of the lens after a number of cleanings.
A number of contact lenses are made of low surface energy polymeric materials. A number of these materials are partially or totally composed of organosilicon compounds such as polyorganosiloxanes which improve the oxygen permeability of the contact lens. For the purposes of this invention, the term "low surface energy material" means a material having a surface energy of less than about 40 dynes/square centimeters in accordance with its art recognized meaning. The higher the surface energy, the more wettable the material is by polar liquids. Examples of contact lenses which are completely composed of polyorganosiloxanes are found in U.S. Pat. No. 3,228,741 to Becker (issued Jan. 11, 1966 ) and U.S. Pat. No. 4,198,131 to Birdsall, et al. (issued Apr. 15, 1980) and examples of contact lenses which are composed of a copoymer of at least one aliphatically unsaturated organic compound such as methyl methacrylate or 2-hydroxyethyl methacrylate and at least one aliphatically unsaturated organosilicon compound (i.e., compounds containing one or more silicon atoms per molecule) are found in U.S. Pat. Nos. 3,808,178 to Gaylord (issued Apr. 30, 1974); 4,153,641 to Deichert, et al.; 4,291,953 to Covington (issued Sept. 29, 1981); and 4,419,505 to Ratkowski, et al. (issued Dec. 6, 1983).
Lipid deposits on low surface energy polymers, particularly the silicone-containing polymeric materials, are especially troublesome because hydrocarbon radicals such as methyl and phenyl radicals attached to silicon atoms are hydrophobic and tend to attract nonpolar lipids. In the case of silicone elastomer contact lenses of the Becker type above which have been surface-treated by the plasma treatment process described in U.S. Pat. No. 3,925,178 to Gesser, et al. (issued Dec. 9, 1975) to render the contact lens hydrophilic, only the surface is hydrophilic (i.e., wettable by tear fluid). The underlying subssantially polydimethylsiloxane elastomer core is very hydrophobic and lipids tend to not only attach to the surface, but also tend to be absorbed into the hydrophobic core. This absorption further complicates the removal of these deposits and may induce further accumulation of lipid deposits which are not adequately removed by currently available cleaning solutions and techniques and thereby shortening the useful life of such contact lenses. Use of abrasive cleaners or vigorous rubbing could remove the thin hydrophilic surface on such lenses and thereby expose the untreated underlying elastomer and render the lens surfaces hydrophobic (i.e., non-wettable by tear fluid) and nonusable.
There is a need for a method of cleaning lipid deposits from contact lenses, particularly those made of organosilicon compound-containing polymeric materials, which removes lipid deposits present on the lens surfaces and, preferably, within the material itself without permanently affecting the physical and optical properties (including color if tinted) of the contact lens and without causing the contact lens surfaces to lose their wettability to any significant degree. The cleaning medium used should also be substantially non-irritating to the eye and is sufficiently volatile to enable the medium to be removed from the contact lens along with the lipid deposits.
As will be explained further, the object of the present invention is to satisfy the aforementioned needs through the use of a contact lens cleaning medium comprising a volatile methylsiloxane fluid selected from the group consisting of certain volatile cyclic polydimethylsiloxanes, linear polydimethylsiloxanes, and branched methylsiloxane fluids which are at least as volatile at room temperature as decamethylcyclopentasiloxane such as the presently preferred octamethylcyclotetrasiloxane. The contact lens is contacted with the medium for a sufficient amount of time to permit the lipid deposits present to be removed from the surface of the lens and then the medium and the deposits associated with it are removed from contact with the lens.
For example, a plasma surface-treated hydrophilic polydiorganosiloxane elastomer contact lens containing lipid deposits can be immersed in a container of neat octamethylcyclotetrasiloxane medium for up to 30 minutes to remove the lipid deposits. It is withdrawn from the medium and excess medium is removed by shaking the contact lens and/or by rinsing the surface of the contact lens with a biocompatible aqueous medium to remove at least a portion of the cleaning medium and the lipid deposits associated therewith. The biocompatible aqueous medium can be, for example, water or isotonic saline solution. The lens is then placed in floating contact with water to permit the remainder of the medium to leave the lens material. After the medium and deposits are removed, the contact lens remains hydrophilic.
In an alternative embodiment of the method of the present invention, the volatile methylsiloxane fluid is dispersed in an aqueous medium to form an emulsion in which the volatile methylsiloxane fluid is the dispersed phase and the emulsion is either rubbed on the surfaces of the contact lens or the lens is immersed in the emulsion medium to remove the surface lipid deposits. The emulsion medium is then removed as above.
It is thought to be novel that the aforementioned methylsiloxane fluids would be useful in cleaning a hydrophilic contact lens without rendering its surface hydrophobic since it is well known that contaminants can render the surface of such lenses non-wettable. It is well known to use higher molecular weight silicone fluids to render the surfaces of substrates such as glassware water-repellent and hydrophobic by using, for example, a polydimethylsiloxane fluid which is sufficiently nonvolatile to leave a fluid film on the surface of the substrate.
Dow Corning Corporation of Midland, Michigan formerly sold an eyeglass cleaning and polishing tissues and fluid which contained methylsiloxane fluids under the name SIGHT SAVERS.RTM. Silicone Treated Tissues and Liquid for use in cleaning hard glass and plastic spectacle and safety goggle lenses to remove grease and grime (e.g., cutting oils), to prevent steam-up, and to clean and polish the lenses. Some of the advertisements refer to leaving a coating of silicone on the lens surfaces to provide extended protection. See British Patent No. 1,295,611 (published Nov. 8, 1972) to Dow Corning Corporation for silicone-treated cleaning tissues for eyeglasses which use a siloxane-glycol copolymer as the cleaning and antifogging agent while U.S. Pat. No. 3,433,667 to Gergle, et al. (issued Mar. 18, 1969) teaches a polishing cloth containing partially cured methylsiloxane fluids and discusses methylsiloxane fluid-treated polish cloths as part of the prior art.
U.S. Pat. No. 2,993,866 to Vaughn, et al. (issued July 25, 1961) describes an aerosol spectacle cleaner containing a volatile alcohol and a siloxane fluid wherein the siloxane fluid is said to cooperate with the alcohol in the cleaning operation, particularly to aid in dissolving organic soils such as fingerprints, "fatty exudations from the skin and hairs around the eyes," and the like from the spectacles. U.S. Pat. No. 2,955,047 to Terry (issued Oct. 4, 1960) teaches cleaning compositions which contain 0.1 to 5% of a polydimethylsiloxane oil which is said to leave a film on the surface being cleaned and is used to improve the cleaning properties of the compositions in terms of wipe-off, soil removal, and ease of cleaning. The low surface tension of the dimethylsiloxane oil is said to enhance the wetting, adherence and spread of the cleaning composition of glass, wood and metal. In each of the foregoing patents, the siloxane fluids used tended to be high enough in viscosity (generally greater than 10 centistokes at room temperature where viscosities were mentioned) that the fluids were relatively nonvolatile since this would be desirable where a lasting film of the material is to be left behind. See Dow Corning Corporation Data Sheet No. 22-0696 dated 8-74 entitled "DOW CORNING.RTM. 200 FLUID" showing that above 10 centistokes in viscosity, only 10% or less by weight of the fluid is lost after 24 hours at 150.degree. C. Use of such fluid to clean a contact lens would not be desirable in spite of the grease cutting ability of the siloxane fluids.
Kasprzak, in U.S. Pat. Ser. No. 670,195 filed on Nov. 13, 1984 which is assigned to Dow Corning Corporation, Midland, Mich., teaches the use of volatile polydiorganocyclosiloxanes to remove grease from fabrics, but this does not suggest contact lens cleaning use since maintaining the hydrophilicity of a fabric does not seem to be critical in that application whereas it is in a contact lens cleaning application. Dow Corning Data Sheet No. 22-904-82 teaches that hexamethyldisiloxane, and the cyclic polydimethylsiloxane fluids DOW CORNING.RTM. 244 and 344 Fluids (octamethylcyclotetrasiloxane) and DOW CORNING.RTM. 245 and 345 Fluids (decamethylcyclopentasiloxane) are useful in a number of cosmetic and personal care formulations, but does not suggest use of these fluids as a cleaner for wettable contact lenses. That Data Sheet does describe the fact that the fluids are compatible with various stearates and other cosmetic ingredients. U.S. Pat. No. 4,324,595 to Kasprzak (issued Apr. 13, 1982) teaching the use of volatile methylsiloxane fluids to remove tacky adhesives from the skin similarly fails to teach the method of the present invention.